Block of 200+ flats, eleven single channel hot water timers blown this week alone.

[GBDamo]

Thanks guys.

Getting stuck into some tinnys now so will pick this back up tomorrow.

Cheers

 

[GBDamo]

My thinking of what we have so far.

The catastrophic failure or the MOV (thanks) in the controller would point to a large over voltage situation.

It is most probably not environmental but a lost Neutral.

Without further information this could be anywhere internal or external.

So I was thinking to approach it on two fronts, to contact the DNO and report a possible Neutral fault whilst surveying the site, reported faults and drawings to see if a pattern can pinpoint the location.

So in a normal fault free situation the installation should look like.

If the fault is in the below position then I should only be hearing of power outages in flats 7, 8 & 9 but not over voltages or the MOV failures I'm seeing.

If the fault is in the below position then flats 4, 5 & 6 and flats 7, 8 & 9 will see voltage fluctuations between 0V and 400V depending on their respective loads, this situation could cause the MOV failures.

And finally, in the below image the fault would be evident across all phases and all flats with under and over voltages. Whilst there are sections of the internal installation that could contain the fault; in this scenario the fault could also be external.

Ii actuality I have already informed the client of the liklihood of a serious fault existing and that it may be internal or external and they will be picking it up from here.

I'm quite disappointed really as its quite interesting to see how far you can fault find on paper if you have enough information.

 

[Lucien Nunes]

Your explanation of the possible scenarios is correct but the configuration in pic.3 is unlikely to exist in practice. Each single phase service will be derived from a 3-phase busbar, with neutrals normally serving one or three phases but seldom two.

If the fault was a cable strike, the neutral may have not merely been broken but also shorted or arced over to a line. A variety of different voltages may have been impressed on the loads in quick succession as the fault developed.

 

[LukeD]

I am loving this thread...some very clever replies

 

[marconi]

I don’t think the burned out disc is an MOV. The timer uses a transformer less way of producing low voltage dc to operate the electronics. I reckon one can see a bridge rectifier - the white block component, and a disc capacitor in series with a resistor of suitable power rating together forming a mains to low voltage dropper. The placement of the resistor and the disc capacitor makes me think their right hand ends are connected to Lin and Nin respectively and their left hand ends to the ac inputs of the bridge rectifier which are normally the inner two leads for this style of rectifier. There is a smoothing capacitor to the left of the bridge rectifier. I reckon the gold rimmed cylindrical component above the relay is a battery for keep alive in the event of power cut and accumulator to handle short duration current surges when the relay turns on.

 

[Strima]

I don’t think the burned out disc is an MOV. The timer uses a transformer less way of producing low voltage dc to operate the electronics. I reckon one can see a bridge rectifier - the white block component, and a disc capacitor in series with a resistor of suitable power rating together forming a mains to low voltage dropper. The placement of the resistor and the disc capacitor makes me think their right hand ends are connected to Lin and Nin respectively and their left hand ends to the ac inputs of the bridge rectifier which are normally the inner two leads for this style of rectifier. There is a smoothing capacitor to the left of the bridge rectifier. I reckon the gold rimmed cylindrical component above the relay is a battery for keep alive in the event of power cut and accumulator to handle short duration current surges when the relay turns on.

A picture of the underside of the PCB would be handy.

 

[GBDamo]

A picture of the underside of the PCB would be handy.

Was dreading that request, damn thing was riveted in.

 

[Lucien Nunes]

The white block will be the dropper capacitor, the bridge rec will be SMD. But yes, let's see some pics of the PCB

 

[marconi]

I was wrong ?

 

[GBDamo]

I was wrong ?

Damn, was hoping my initial guess was a stroke of genius.?